The present invention relates to tire retreading, and more particularly, it relates to a radially expandable and contractible rim for securing an annular elastomeric member against a tire bead.
Tire retreading, or recapping, may be applied to any size tire casing but is more commonly used on radial truck tires. The casings of these tires usually have a longer useful life than their treads. Therefore, it is often more cost effective to retread a worn casing than to replace it with a new tire.
One known process simultaneously bonds and vulcanizes uncured rubber on a worn tire casing in a tread forming mold. In another known process, a precured rubber strip with a premolded tread is wrapped around the buffed crown surface of the worn tire casing with a bonding agent such as uncured rubber or cushion gum disposed therebetween. The assembly is then sealingly enclosed in an annular elastomeric curing envelope of U-shaped radial cross section typically of thin synthetic rubber, or the like as manufactured by Presti Rubber Products, Inc. of New Britain, Pa. The annular space between the tread and the envelope is evacuated, thereby stretching the outer envelope into intimate contact with the outer sidewalls of the casing and all surfaces of the tread strip. This ensures that uniform pressure is applied over the entire bonding area without tread distortion during the curing process. The outer envelope also prevents air and steam from becoming entrapped between the tread strip and the casing and migrating into the bonding agent. The entire assembly is then placed in a curing chamber, or autoclave, at elevated temperatures and pressures to vulcanize the uncured components and to positively bond the casing and tread strip together. The outer envelope is then removed for reuse if desired.
Outer curing envelopes as described are not as easy to install as desired, especially when smaller inside circumference envelopes need to be pulled over the outside circumference of large truck tire casings. Therefore, various special mountings, rims, and linings have been developed to facilitate sealing of the curing envelope around the tire casing and tread assembly.
In one known commercially available arrangement, the side skirts of the outer curing envelope are made longer than the sidewalls of the tire casing with which it is to be used. The excess margin of the outer envelope, i.e., the margins adjacent to the inner peripheries of the skirts, are tucked inside the tire beads and held in place by a radially-expandable rim. In this arrangement, the inside surface of the tire casing is exposed while the entire outside is encased.
Another arrangement involves the use of sealing rings with an outer curing envelope as described in U.S. Pat. No. 5,098,268 to Robinson.
Known radially-expandable rims typically are constructed of a metal band having a locking device which adjusts the rim to an initial relaxed circumference smaller than the bead circumference of the tire to be retreaded and to an expanded circumference which is larger than the bead circumference.
Known rims, however, cannot be incrementally adjusted in size from the initial relaxed circumference to the expanded circumference to account for different tire bead circumferences. Most known rims rely on spring compression to expand the ring and, thus, require good hand and arm strength to mount the rim against a tire bead and to dismount the rim after retreading is complete. In addition, some expandable rims do not maintain a constant circular shape and instead become slightly elliptical during the retreading process. Elliptically shaped rims can allow flaws to occur in the retreaded tire during the curing process. Thus, a need exists for a radially expandable and contractible rim for use to secure an annular elastomeric member against a tire bead during tire retreading which is incrementally expandable and retractable, which is easy to mount against and dismount from a tire bead and which maintains its circular shape throughout the retreading process.